Asterisk chan_alsa: /dev/snd/ permission denied

Installing and Using OpenWrt
1

I am trying to set up Asterisk chan_alsa with a USB sound device which I plan to use as a SIP client (softphone).

opkg install kmod-usb-audio kmod-sound-core usbutils asterisk16-chan-alsa asterisk16-app-senddtmf alsa-utils shadow-usermod

Edited /etc/asound.conf to contain

pcm.!default {
    type hw
    card 0
}

ctl.!default {
    type hw
    card 0
}

With this brute force method I get it to work:

root@Asterisk:~# chmod -R 777 /dev/snd/
root@Asterisk:~# chmod -R 777 /dev/audio 
root@Asterisk:~# /etc/init.d/asterisk restart
root@Asterisk:~# asterisk -rvvvvvvvvv

console dial 6000@default
console hangup

But that is probably not the way to do it. How to do this correctly?

The following works once but stops working as soon as I unplug and replug the USB sound device:

root@Asterisk:~# usermod -a -G audio asterisk
root@Asterisk:~#  chown -R asterisk /dev/snd
root@Asterisk:~# /etc/init.d/asterisk restart
root@Asterisk:~# asterisk -rvvvvvvvvv

console dial 6000@default
console hangup

How can I tell the system that the asterisk user is allowed to use /dev/snd permanently?

I guess root@Asterisk:~# sed -i -e 's|audio|asterisk|g' /etc/hotplug.json is not the way to go either? Although after a reboot it seems to "work"...